This proposal comprises an application for a Clinical Scientist Development Award for Dr. Michael Kapiloff, a pediatrician and molecular biologist, currently performing research at the Vollum Institute of the Oregon Health Sciences University. Dr. Kapiloff is seeking funding for a period of training under Dr. John D. Scott. Mentoring by Dr. Scott should allow Dr. Kapiloff to transition successfully to the role of an independent principal investigator who studies the regulation of signal transduction in the heart. Signal transduction of extracellular stimuli occurs in part through the phosphorylation of intracellular proteins. A fundamental question in the field of signal transduction is how signaling by protein kinases is coherent in the face of many possible substrates that these enzymes are able to phosphorylate. Specificity in signaling is maintained in part by the spatial segregation of protein kinases. At the molecular level, targeting of kinases to intracellular structures is mediated by anchoring proteins. This concept is pertinent in the heart where cAMP mediates the effects of beta-adrenergic stimuli in regulation of ionotropy, chronotropy, and hypertrophy. I have recently cloned an A kinase anchoring protein called mAKAP that targets the cAMP-dependent protein kinase (PKA) to the nuclear membrane (NM) of differentiated cardiac myocytes. We propose that mAKAP functions to direct the localization of PKA to the NM where the kinase is positioned to selectively phosphorylate substrates in that vicinity. I have shown that mAKAP is targeted to the NM by a domain containing repeat sequences similar to those in dystrophin and spectrin. In Specific Aim number 1, we propose to determine what protein(s) binds the mAKAP targeting domain at the NM. Further, we propose to identify other mAKAP binding-partners which might constitute a functional complex. In Specific Aim number 2, we propose to test the role of mAKAP in cAMP and calcium-regulated transcription factor activation and gene expression. In Specific Aim number 3, we will address the possibility that the human mAKAP gene is mutated in a cardiac disorder to which it shares genetic linkage, arrhythmogenic right ventricular dysplasia. In collaboration with Dr. Luisa Mestroni, we are investigating whether mutations of mAKAP, which is poised to have a direct impact on cardiac nuclear function, are responsible for a clinical disorder which can result in cardiomyopathy and sudden death.